Fiber Optic Gyroscopes (FOGs) have been used to measure rotation rates or changes in angular velocity about an axis of rotation. A basic conventional fiber optic gyroscope (FOG) includes a light source, a beam splitting device, a coil of optical fiber and a system photo detector. The beam splitting device splits light from the light source into separate beams that propagate through the coil in counter-propagating directions and eventually converge at the photo detector. The rotational rate of the coil can be determined based on optical characteristics of the light received at the photo detector such as interference caused by the Sagnac effect, for example. In certain applications, the optical characteristics of interest require only very little optical power to be received at the photo detector to meet the performance requirements of the FOG. Besides reducing power consumption and heating effects, operating at a low optical power reduces bias instability due to non-linear optical effects. However, over the life of the FOG, the optical circuit develops more optical loss, meaning less optical power generated by the light source actually arrives at the photo detector. As less light is received at the photo detector, the sensor becomes less sensitive to rotation, exhibiting reduced rotation signal-to-noise ratio. When the light beam is transmitted at only a low optical power at beginning of life to mitigate nonlinear optical errors, relatively little margin is available to account for optical circuit aging before the sensor can no longer meet performance requirements.
One potential solution for this problem is to use digital electronics to increase occasionally the optical power output of the light source as the optical circuit becomes more lossy, to maintain a relatively constant optical power level as received at the photo detector. As practiced in the art of FOGs today, light sources are driven using very stable power references so that their optical power output is as constant as practicable, even though this does not result in a stable power level as received at the photo detector. This is because fluctuations in light source optical power can produce errors such as scale factor shifts in a FOG. In a similar way, introducing finite-step adjustments in optical power to address optical circuit aging may generate unacceptable scale factor errors within the gyroscope. For example, if a relatively common digital-to-analog converter (DAC) (having 12 bit resolution, for example) were used to generate a feedback signal to control the light source, the resulting step errors produced within the gyroscope would be intolerable for many applications. While higher resolution DACs can be employed, such devices require correspondingly larger footprints and power, and generate more heat.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved systems and methods for optical power control in fiber optic gyroscopes.